1. Field of the Invention
This invention relates to window systems, and more particularly relates to energy-saving windows using diffraction gratings and spectrally selective coatings in a manner which controls the entry of selected sunlight components, notably heat and light, into a room.
2. Description of Related Art
Window efficiency has a significant impact on energy consumption in both residential and commercial buildings. Windows also affect the thermal and visual comfort of the building occupants. The overall figure of merit for the performance of a window system is a complex function dependent on many variables, including type of building, climate, orientation, and type of use. Whereas for residential buildings the primary and well known element in efficient window design is heat loss control and transmittance of visible daylight, an equally or more important concern for all windows taken in aggregate is efficient, fully dynamic control of solar heat gain, especially in the United States where a majority of regions have plentiful sunlight. This is so because of the greater cost of cooling, both in energy consumption and heating/ventilation/air-conditioning (HVAC) system installation.
A wide variety of techniques have been developed and used for control of solar luminous transmittance, solar heat gain and interior heat loss through windows in residential and commercial buildings. These include fixed and adjustable mechanical methods such as shades, blinds, fins, awnings, slats and louvers; conventional optical techniques such as use of colored low-transmittance glasses; spectrally selective coatings of of single metal layers and dielectric-metal-dielectric multilayer stacks; and chromogenic single- or multilayer structures based on photochromic, thermochromic and electrochromic phenomena. Most of these existing methods have focused on one or more, but not all, features one desires to have in an ideal window, namely. optimum utilization of the luminous portion of the solar radiation, control of the solar infrared radiation, effective heat loss control of the interior heat in winter months, reduced cooling loads in summer months, reduced electrical lighting loads, dynamic control as a function of daily or seasonal climatic variations, user modifiability of optimum parameters, aesthetics of appearance, and, perhaps most importantly, low production costs.